Add testee to devDependencies

Author: chasenlehara

package.json

@@ -21,7 +21,8 @@
     "react-dom": "^16.12.0",
     "steal": "^2.2.4",
     "steal-qunit": "^2.0.0",
-    "steal-tools": "^2.2.2"
+    "steal-tools": "^2.2.2",
+    "testee": "^0.9.1"
   },
   "scripts": {
     "build": "node build.js",